Many digital serial telecommunications signals have a frame structure, with some bit positions within the frame designated to carry payload data, and some bit positions designated to carry transport overhead. Transport overhead includes administrative information needed to successfully transport the payload data, such as parity and frame synchronization data.
A circuit that receives a serial bit stream typically contains a frame synchronizer that monitors the incoming bit stream, finds the frame synchronization pattern, and provides a frame synchronization signal to the rest of the circuit. The frame synchronization signal is based on the position of the frame synchronization pattern within the frame, and is used by the rest of the circuit to extract payload and overhead data from the bit stream.